Optical emission spectroscopic study of plasma plumes generated by IR CO₂pulsed laser on carbon targets

Abstract

Optical emission spectroscopy studies, in the spectral range ultraviolet-visible-near infrared (UV-Vis-NIR), were performed to investigate thermal and dynamical properties of a plume produced by laser ablation of a graphite target. Ablation is carried out using a high-power IR CO 2 pulsed laser at λ = 9.621 µm, power density ranging from 0.22 to 5.36 GW cm −2 and air pressures around 4 Pa. The strong emission observed in the plasma region is mainly due to electronic relaxation of excited C, ionic fragments C + , C 2+ and C 3+ and molecular features of C 2

Temporal evolution of the laser-induced plasma generated by IR CO2 pulsed laser on carbon targets

“…These spectra ͑not shown͒ reproduce particular emission of carbon plasma in a mediumvacuum air atmosphere. 26,27 From all these spectra we can observe that the intensity of ionic species ͑C + , C 2+ , C 3+ , N + , and O + ͒ increases up to ϳ1 s and decays rapidly at high delay times. Above ϳ4 s these species are not observed.…”

“…At distances close to the target surface ͑Ͻ9 mm͒, all of the emission lines of C, C + , C 2+ , and C 3+ expected in the 2000-10 000 Å wavelength range are observed, 26 illustrating that the excited species giving rise to the optical emission are produced by a nonspecific mechanism during the TEA-CO 2 laser ablation process. However, a direct excitation-de-excitation mechanism cannot explain the observed emission spectra.…”

“…͑1͒ and relevant parameters involved in the calculation of excitation temperature can be found in our previous paper. 26 Real plasmas provide, even in the worst cases, just an approximation to LTE. However, their spatial inhomogeneity is very large as concerns the temperature and number density distributions of the different species.…”

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] The wavelength and spatially resolved measurements of emission spectra of the CO 2 laser ablation plume at the carbon target have been reported recently by us. 26,27 The present paper is aimed at discussing thermochemical processes produced by a high-power IR CO 2 pulsed laser on graphite target and at evaluating laser ablation induced changes, which are of fundamental importance in establishing the mechanisms responsible for the plasma emission. In this work we present some new results obtained from the time-resolved spectroscopic analysis of the PLA plume.…”

Effects of a static inhomogeneous magnetic field acting on a laser-produced carbon plasma plume

“…In particular, our results show that in a vacuum background the presence of the magnetic field plays an equivalent role to that of a low pressure neutral background gas, in order to favor the emission of successive plasma fronts and C 2 molecules formation, as reported previously in investigations of laser produced carbon plasmas. 4,5,[17][18][19][20] …”